Missed the mark on your last trail run? If you've been training indoors, blame your treadmill.

Thatís because running on rough or uneven terrain outdoors takes 10 percent more energy than plodding along on your smooth treadmill, says the studyís lead researcher, Luigi Fattorini, a professor at the Sapienza University of Rome. Throw in the wind and you really need to crank up the slope: If there's a gentle breeze at 9 miles per hour, you expend 5.5 percent more energy than you would without wind.

Your move: To prepare for a race, train at an incline of 3 percent or higher -- and when possible, train in the same type of shoe you plan to race in. (Need suggestions? Check out The Best Running Shoes For Men.) Researchers in the study had people wear running shoes on the treadmill, but measured their outdoor caloric burn while they wore trekking boots. Switching up your shoes can throw off your time since shoes with greater ankle support -- like most hiking boots and many trail running shoes -- limit your ankle flex, can make you less efficient, and force you to work harder.
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Can you vouch for the above? I don't run on treadmills. For one, only a few places would let me run shirtless inside their establishment (despite having shirtless pictures of men all over the place) and second, I would miss seeing all the girls when I run outside. Even during the winter time I don't let the cold stop me from running shirtless. In fact, running shirtless during the cold months actually increases the attention and yelling so I'm there!

I have found it to vary quite a bit from threadmill to threadmill. However, if you are used to running with a GPS or on tracks, you'll instinctively know app. how fast you're going. My local gym has some really slow threadmills. 11 km/h on them is the same intensity as 13 km/h on the tracks. However, I've also run on some threadmills that are a couple of km/h faster than outdoor. I am comparing it with running on tracks, which is faster than running in terrain since you don't have any unevenness.

Yeah, I recently (well like 6 months ago) switched from running on a treadmill to running on a track outdoors, and definitely noticed a difference. It took me a month or 2 running outdoors to be able to match what my treadmill had said I was doing.

It depends on the outdoor track. Here in Seoul I usually run on Namsan, which is quite tough because of the hills, and I notice that I can beat my 20k long run time by about 15 minutes on a treadmill (10k about 5 minutes). Back home in Canada, on flat Saskatchewan terrain, treadmill time is about equivalent. Incline definitely helps if you're stuck on a treadmill, although I think it's better to change it up instead of keeping it on 3%.

I just can't run on a treadmill. I've tried it, but the stride is too unnatural for me. The mat moves back with such force that it creates a lot of stress on my knees.

I prefer hiking. I've gone out in the mountains here on 5 consecutive days, and most of it was jogging, 7 hours per day with just a short break for lunch (I always carry an 18L pack since I don't camp out, with a 2L bladder of water. Light enough to cover a lot of terrain, but enough gear to survive the night if something happens). Much more relaxing and rewarding than a session on a treadmill, and a far better workout, too.